Shared connected customer electronics devices like a television (TV), digital video recorder (DVR), a Blu-Ray player, or other set-top box may be running applications that require accessing personal content like user photos, e-mails, news, or personalized TV program recommendations.
Shared devices, by definition, are shared among multiple users (family or housemates). Therefore, one user's content may be exposed to other users leading to private information leaks and presenting inappropriate or wrong data. Therefore, mechanisms must be used to determine who is currently using the shared device. Moreover different users may/or may not want shared-device applications to use their accounts or only want the shared-device applications to use their accounts under certain conditions.
These mechanisms should not involve typing a password with every user change as this can happen very often with televisions. Televisions and many other shared devices usually do not have convenient keyboards and therefore typing complex passwords may be difficult. Because the shared devices are shared by many people who may watch the user's hands or the screen, typing the password can be risky.